It is possible to experience a short time where your service will be interrupted. This gap could occur between the cancellation of your current service and the activation of your new broadband plan. To ensure the switch will be as seamless as possible, you can cancel your current contract after the new one is activated. However, if the providers use the same network, you should expect to see no interruption.
If the old operator and new provider are using different networks or technologies, you may need to cancel the current service yourself. If you know the exact date of your new service going live, then you can arrange to cancel your existing service a few days later. However, it is important to check your contract because most providers require a 30-day notice, and some request this in writing.